The present invention relates to a sealing nozzle arranged in a blow box used in the drying section of a paper machine defined in the preamble of the first claim presented below.
In the drying section of a paper machine the web is conveyed in a known manner by using either a single or a twin wire run. Single wire run means such a run where the web passes from one drying cylinder to the next supported by a single drying wire; the web passes also between the drying cylinders supported by the same wire. The web passes over the drying cylinder between the cylinder and the drying wire.
Twin wire run means such a run where separate top and bottom wires are used to support the web when it passes alternately over the lower and alternately over the upper drying cylinders. Also in this case the web passes over the drying cylinders between the cylinder and the drying wire. However, from an upper cylinder to a lower cylinder, or in the opposite direction, the web passes partly free, without support. The guide rolls of the drying wires are often located so that the wire and the web would disengage simultaneously from the drying cylinder, and so that the wire supports the web over a short distance as it passes from one cylinder row to the next.
In ever faster paper machines it has become a problem in that the web tends to become detached from the surface of the drying wire, at a point where the wire and the web together should travel from a drying cylinder to a redirecting cylinder or a guide roll located at a lower level.
The disengagement of the web from the wire leads easily to a wire break, or at least to the wire forming sacks or folds. The disengagement of the web from the wire leads thus to runnability problems, which are further emphasized when the speeds of the paper machines increase.
It is previously known, for instance from U.S. Pat. No. 4,905,380, to use different blow boxes in order to improve the runnability of a paper machine. The ejection blow created by the blow box induces a negative pressure region in the gap space between the drying wire and the wall of the blow box, and this negative pressure region keeps the web attached to the drying wire when the web passes from the drying cylinder to the guide roll below the cylinder.
However, a problem in the above-described solution is to have the negative pressure region induced by the blows safely sealed from the region left outside of the negative pressure region. In connection with running disturbances paper waste is generated, which as so called paper lumps or paper clumps are entrained by the web also to the blow boxes. Due to these bulges present in the web a blow box cannot be mounted at a short distance from the wire run, which would be optimal regarding the sealing. The blow box must be mounted at a certain safe distance, which is typically &gt;50 mm, in which case the negative pressure region is not sealed in the best possible way. The effects of the ejection blows are also often insufficient when the blow nozzles of the blow boxes must be located at said safe distance from the wire.
It is known as such, for instance from U.S. Pat. No. 4,996,782, to use pivotable flaps to direct the air blows to a desired object, where the air is wanted to flow through the wire in order to ventilate the pocket formed by the wire loop. The object of the flap is not to seal the gap between the blow box and the wire.
The object of the present invention is to provide an improved sealing nozzle for the blow box in a paper machine.
An object is particularly to develop the previously known blow box solution so that the negative pressure effect can be even further intensified during the run.
An important goal of the invention is also to provide such a sealing nozzle of a blow box, with which the air blows providing the negative pressure, are generated as close as possible to the supporting fabric of a paper machine, such as a wire, moving past the blow box, and which nozzle is available both during the normal run and the threading.
A further object of the invention is to provide a sealing nozzle for a blow box which can be safely brought very close to the wire in order to provide ejection blows or ventilation of the pocket. Then an object is particularly to provide a sealing nozzle with a blow which can be directed accurately and which can provide the required pressure differences, however, retaining the operating safety of the structures.
In order to achieve the above-presented objects the new sealing nozzle for a blow box in the drying section of a paper machine according to the invention is characterized in what is presented in the characterizing part of the first claim presented below.
A typical blow box in which the invention is applied and used in the drying section of a paper machine is arranged in said drying section in the pocket space defined by the wire passing from the first drying cylinder to the second drying cylinder and a redirecting member arranged in this wire run, such as a redirecting cylinder, a guide roll, a suction roll or the like, in order to eject air away from said pocket space and to create a negative pressure region in at least a part of this pocket space. In the blow box, at the border between the desired negative pressure region and the region outside it, there is arranged one or more sealing nozzles according to the invention projecting from the blow box against the wire up to a certain distance "d" as seen from the wire, in order to create a seal between the negative pressure region and the region left outside the negative pressure region. Said sealing nozzle is advantageously combined with the blow box so that the member can be moved away from the wire by pushing or with the aid of an actuator, to a distance "d'" which is larger than the distance "d".
In this description of the invention and in the claims a blow box means typically box-like structures extending across the web or even structures of other shapes extending across the web, such as beam-like or tube-like structures, with which ejection air can be supplied into the pocket or a part of it.
A wire in this description means typically a drying wire, a felt or another corresponding fabric, with which the web is supported, for instance when the web passes over a drying cylinder.
The invention is applicable in the drying sections of paper machines utilizing both single wire runs and twin wire runs. In drying sections provided with a single wire run a blow box using a nozzle according to the invention can be used to create a negative pressure region and to seal it both in the travel direction in the region of the wire run from the first drying cylinder, or in the region called the "inlet side" in this description, and in the region of the wire run going to the next drying cylinder, or in the region called "outlet side" in this description, when the blow box is arranged in the pocket space defined by two drying cylinders, the wire runs between them and the redirecting cylinder below them.
In drying sections provided with twin wire runs a blow box according to the invention arranged in the wire pocket space defined by two drying cylinders, the wire runs between them and the wire guide roll, can be used to create a negative pressure region and seal it in the region of the wire run coming from the first drying cylinder, or at the inlet side. In the region of the wire run to the next drying cylinder, or on the outlet side, the blow box can be used to generate blows causing ventilation of the pocket.
The sealing solution according to the invention could of course be used also more generally in a paper machine or the like at a supporting fabric or e.g. at a roll, for preventing air from entering between this supporting fabric or roll and the blow box by ejecting air away from this intermediate space.
In an advantageous embodiment of the invention the sealing is conducted with a sealing nozzle having a sealing member which is arranged very close to the wire, and the actual nozzle part of the sealing member blows air from the blow box along the convex outer surface of this sealing member, in other words, along the convex surface which faces the wire. With this sealing nozzle air is blown on the inlet side of the wire, advantageously so that the air blow meets the wire before the wire disengages the cylinder located before the pocket, in which case the cylinder surface behind the web prevents the web from being disengaged from the wire due to the blow. Air is correspondingly blown with a sealing blow nozzle on the outlet side, so that the air meets the wire only when the gap between the wire and the cylinder after the pocket has closed, in which case the blow will not disengage the web from the wire.
A blow box according to the invention is typically arranged at a safe distance from the wire, which safe distance in a single wire run ranges typically between about 25 and 50 mm, and in a twin wire run &gt;50 mm, even 100 mm. On the other hand, during normal run the sealing member according to the invention can be brought even closer than 15 mm from the wire, typically about 3 to 15 mm, advantageously to a distance of 5 to 10 mm. In this way the negative pressure effect created by ejection between the blow box and the wire can be intensified, and the gap can be sealed between the created negative pressure region and the region left outside the negative pressure region. The sealing member is flexible, pivotable or otherwise movable, so that when a paper lump or the like pushes the wire toward the blow box the sealing member can turn or move to a distance "d'" &gt;20 mm, typically 20 to 50 mm, from the wire. This distance "d'" can be considered sufficient; the distance allows generally the paper lumps in question to pass the blow box without causing damage to it.
On the other hand, the sealing member can be integrated with an actuator, which in advance moves the member a short distance away from the position close to wire, if it is anticipated that wrinkled paper and paper lumps are entrained with the web in larger amounts than normally. During threading the actuator can move the sealing member to a distance of &gt;20 mm, typically about 20 to 30 mm from the wire.
According to an advantageous embodiment of the invention the sealing member according to the invention is connected to a stationary blow box with the aid of a joint mechanism.
The nozzle part is typically formed by a nozzle part provided with a slit-like nozzle opening extending across the web, or by several nozzle parts arranged one after another across the web. The sealing blow nozzle is typically arranged in the front part of the gap between the blow box and the wire loop, as seen in the travel direction of the wire, in which case air can be ejected away from this gap with the aid of the sealing nozzle, and thereby the interfacing region extending across the web and formed in this way between the negative pressure region and the region left outside this negative pressure region can be sealed.
A blow box according to the invention can be formed mainly by a single uniform basic air box extending across the web, in which air box a sealing nozzle is arranged for blowing air and for sealing the negative pressure region at least on the inlet side of the wire run, when the inlet side refers to that part of the wire run where the wire arrives in the pocket. In a single wire run application another sealing nozzle according to the invention can be advantageously arranged on the other side of the blow box for blowing air into the outlet side of the wire run, in other words when it moves from the pocket to the next drying cylinder, in which case the whole pocket region defined by the blow box and the cylinders, the wire runs and the guide roll can be brought into a negative pressure. Whereas in a twin wire run application a conventional blowing nozzle can be arranged, instead of an ejecting nozzle, on the other side of the blow box, in other words on its outlet side, in which case the blowing nozzle creates ventilation on this side of the blow box.
A blow box according to the invention is often a box of the whole pocket, which, when the safety distances are observed, occupies substantially the whole pocket space, which is left between the drying cylinders and the redirecting cylinder or the like located overlapping therebelow, and which pocket space is defined by the wire. On the other hand a blow box according to the invention can be formed by two blow box parts located side by side and extending across the web, between which blow box parts a passage is formed, which can be closed with a sealing member, which passage connects the pocket space formed by the blow box and the wire loop with the space outside the wire loop.
The sealing member is advantageously arranged in the pocket on the inlet side of the wire, so that when the nozzle part projects toward the wire, for instance by a spring force, it will turn in a sector located in the travel direction of the wire, as seen from the turning joint. On the wire outlet side the sealing member turns correspondingly in a sector located in the opposite direction, as seen from the turning joint. The actual nozzle part is mounted in the sealing nozzle in the part located away from the turning joint, in other words adjacent the pivotable end of the sealing member. The sealing member is advantageously shaped so that its wall closest to the wire is convex, in which case, when the wire is pushed toward the sealing member it will easily glide past the member and will not be caught by the member, irrespective of the travel direction of the wire. Due to the Coda effect the blows coming from the nozzle part travel in a controlled manner over the convex surface, whereby the blows induce a negative pressure between the wire and the blow box. The air blows coming from the nozzle part also facilitate the gliding of the wire over the member.
A great improvement of the runnability of the drying section in a paper machine is achieved with the sealing nozzle solution according to the invention when the device according to the invention intensifies the negative pressure effect in the wire pockets during operation, and during threading on the other hand a very effective air removal from the pockets is provided. The negative pressure effect provided by the blow boxes can be particularly well intensified when the actual ejecting nozzles can be brought as close as possible to the wire and the web travelling with the wire. The paper web can be kept better attached to the wire on inlet side of the pocket, when the pressure regions of the pockets can be controlled by bringing the ejection air closer to the wire and by sealing the negative pressure regions better than previously from the surrounding air spaces. With the solution according to the invention it is still possible to keep the blow box structures at a suitable safety distance from the wire and to move the blow nozzles safely to the respective required safety distance, either automatically or by using an actuator.
Using the solution according to the invention in a normal single wire run it is often possible to reduce the air volumes in the redirecting suction rolls below the drying cylinders when the negative pressure effect is intensified with a blow box according to the invention in different locations of the pocket space.
According to one aspect of the present invention there is provided a sealing nozzle assembly disposed in the drying section of a paper machine in which a paper web is supported by a supporting fabric and guided over a cylinder so that the web is between the supporting fabric and the cylinder, the supporting fabric comprising a first side opposite the cylinder, and a second side adjacent the cylinder, the assembly comprising: A blow box, having a wall, mounted on the first side of the supporting fabric and spaced a distance D from the supporting fabric so as to define a passage between the blow box and the supporting fabric, the passage comprising a negative pressure region having a border with a region outside the negative pressure region. A sealing nozzle mounted in the wall of the blow box and facing the passage, and spaced a distance d from the supporting fabric. And the sealing nozzle comprising: a pivotal sealing member mounted at the border, and a transverse support element, the sealing member pivotal about the transverse support element; and a separate nozzle part having at least one nozzle opening and disposed in the negative pressure region in front of the pivotal sealing member, the separate nozzle part positioned so that the at least one nozzle opening blows air along a surface of the sealing member from the negative pressure region to the region outside the negative pressure region.
The nozzle part may comprise first and second nozzle lips defining the at least one opening of the nozzle, when the first nozzle lip is between the nozzle opening and the sealing member and is longer than the second nozzle lip. The nozzle may comprise a spring member which biases the sealing member against the first nozzle lip so that a minimal gap is left between the sealing member and the first nozzle lip. The at least one opening may comprise at least one slit substantially transverse to the web, preferably a plurality of successive slits substantially transverse to the web. The blow box may be positioned in a wire pocket formed between first and second drying cylinders in the drying section of the paper machine provided with a single wire run, and the first drying cylinder may have an opening gap, in which case the nozzle part is positioned at the opening gap and downstream of the sealing member in the travel direction of the wire run.